The invention relates to a microfinishing tool comprising a shank, at least one rigid cutter, as well as at least one guide rib on the periphery and a taper screw by means of which the cutting diameter can be adjusted.
Such tools are used especially as reamers.
From CH-PS 449390 there is known a reamer supplied with coolant whose tool body is provided with a central longitudinal bore leading to the cutting head, and from which longitudinal bore a plurality of transverse bores extend outwardly at an angle between the cutters. Coolant and lubricant is supplied through these bores in order to cool and to lubricate the cutting head during the cutting process.
In a reamer having an adjustable cutting head, described in DE 32 34 238 A, the reamer is provided with a central coolant bore which divides into two diverging branch bores skirting the shank of the taper screw at a shallow angle. The taper extends only over the forward cutting region, so that upon adjustment only the forward portion of the reamer is expanded.
According to EP 0215144B, a reamer is provided with a cutting head expansible by a taper screw and with a coolant passage leading axially through the reamer shaft, with the coolant passage extending into a threaded bore receiving the threaded shank of the taper screw and subsequent to this passing into a hollow cylindrical part of the reamer shaft which is expansible by the taper screw. Between the hollow cylindrical shaft portion and the taper screw there is an annular channel which is connected with the axial coolant passage by means of an axially parallel coolant passage in the taper screw. From the annular passage leads at least one channel between the cutters, with this channel or channels being directed forwards at an angle of between 30xc2x0 and 45xc2x0.
CH-PS 645 051 describes an adjustable machine reamer with taper screw which comprises adjustment means for changing the spacing of the cutters and the guide ribs from the reamer axis in the same sense and to approximately the same degree. Again, the adjustment taper extends only over the forward cutting region.
It is the object of the invention to provide a microfinishing tool which is versatile in use, cuts with a high degree of accuracy and can be manufactured economically.
This object is achieved in accordance with the invention by a microfinishing tool as defined herein.
In FR 2460173A there is described a microfinishing tool which has an expandable taper insert which is longer than the cutter. The taper insert is seated in an axial blind bore of the tool shank and has a cylindrical recess in its front end. A radial slot extends from the front end approximately up to the level of the end of the blind bore. Between the cutter and the radial slot there is located a radial screw which is in contact with the taper insert. By rotating the screw one can cause a local asymmetric deformation of the shank, which is weakened in terms of material at this point, and consequently effects a change in the cutting diameter. This arrangement makes possible only a local diameter adjustment and necessitates additional finishing measures and parts. Moreover, it is only suitable for a cutter where the adjustable cutting region is only short.
It is the object of the invention to provide a mircofinishing tool which is versatile in use, cuts with a high degree of accuracy and can be manufactured economically.
A microfinishing tool in accordance with the invention thus comprises a shank, at least one rigid cutter, at least one guide rib on the periphery and a taper screw by means of which the cutting diameter can be adjusted. The taper region of the taper screw is at least equal in length to the cutter.
The term xe2x80x9ctaper screwxe2x80x9d used herein should be understood to include all other expansion parts and arrangements with varying diameter which will achieve the desired expansion effect. By extending the length of the taper and of the taper region one achieves an enlargement of the expansion zone. Consequently, the cutters and/or guide ribs can be expanded parallel to the axis, ie. their orientation to the axis remains unchanged and the tapering of the microfinishing tool is maintained. Because the tapering remains the same in spite of changes in diameter, one achieves an unvaryingly good surface quality with the tool.
Preferably, recesses are provided in the shank of suitable shape to serve as expansion aids in the adjustment of the cutting diameter.
Because of the guide ribs the microfinishing tool has a quiet, stable mode of operation in spite of high speeds of rotation and/or hardness of the workpiece, over its whole diameter range. Preferably, with the microfinishing tool of the present invention, at least one guide rib is provided per cutter. Additionally, a guide rib can be arranged axially offset in relation to the associated cutter.
The cutter and/or at least one guide rib can be made as one piece with the shank as a solid tool. The manufacture of the tool as a solid tool is very advantageous, particularly in solid hard metal. The cutters and/or guide ribs can be inserted, or alternatively the cutters can be soldered on.
The different pressure points of the taper screw make it possible to adjust the cutters and guide ribs in a defined way. Depending upon the lengths of the cutters and guide ribs the pressure points can be located at different diameters and axial positions of the taper screws and thus a desired axial region of the cutters or guide ribs.
The material of the cutters and guide ribs can be chosen so as to be matched to the particular requirements of use, independently of the tool body. For example, guide ribs with minimum lubrication and for high speeds of rotation are preferably made of diamond.
A variation of the taper screw comprises tapered sections having different angles of taper. In this way, the enlargement of the diameter can be effected in steps. The taper screw can alternatively be made as a multi-part component.
In one preferred embodiment of the microfinishing tool in accordance with the invention the taper screw includes a cylindrical section after the threaded region, with this cylindrical section being a snug fit in the shank of the tool. This effects a guidance and alignment of the taper screw and consequently gives an extraordinarily precise, centered expansion of the cutting region, if wanted.
The microfinishing tool according to the invention can be provided with internal cooling for coolant and/or lubricant, which is guided in particular to the cutting zone.
This internal cooling is provided for example as a central axial coolant bore in the tool shank for coolant and/or lubricant. From the central axial coolant bore, at least one branch bore leads outwardly into its forward region. In one embodiment of the internal cooling, the branch bore leads into a coaxial supply bore which extends axially at least partially over the cutting region and from which at least one discharge bore leads to the cutting region. The use of coolant and lubricant having 10% or more of an oil-containing emulsion is particularly suitable.
With the structure of the microfinishing tool in accordance with the invention, coolant and lubricant can be supplied to the cutting zone even if the tool shank has been expanded for example by a taper screw or if several cutters or adjustable cutters are provided. The bore which carries the coolant and lubricant runs through into the forward or cutting region either through a possibly provided taper screw or its receiving passage, so that there is no weakening of the material at this position. Rather, the bore extends coaxially into the cutting region and then in the radial direction in the region of the cutters and guide ribs which are to be cooled or to be lubricated. By the simple channel design, the bore geometry is very simple and consequently can be effected at low cost for the most varied types of friction, sinking and boring tools, even without taper screws. In addition to this, the cooling effect of the coaxial bore feeding the coolant through the tool shank can also be utilised.
In particular, the bore arrangement of the present invention makes it possible to cool and to lubricate even the guide ribs of such a tool, so that one ensures a smooth and trouble-free operation of the tool. Preferably, a discharge bore is associated with each guide rib. The coolant and lubricant can be supplied as desired, and the intermediate spaces between the guide ribs can be cleaned effectively of any remaining chip material, etc.
Preferably, the coaxial supply bore extends over the whole length of the cutting region. In this way, the coolant and lubricant are distributed over the whole cutting region and are supplied to the cutters or guide ribs at desired positions by way of the discharge bores.
A particularly good cooling and lubricating effect is achieved in the microfinishing tool according to the invention if a plurality of axially offset discharge bores are provided. The number and axial arrangement of the discharge bores can be chosen according to the mechanical and thermal load of the cutting region which is anticipated.
Preferably, the discharge bore issues into the chip space of an associated cutter. In this way, the coolant and lubricant goes directly to the cutter to be cooled and the chip material can be freed and carried away.
In one advantageous embodiment of the microfinishing tool according to the invention, the discharge bore associated with the guide rib leads outwards in the direction of rotation in advance of the guide rib, i.e. the coolant and lubricant goes directly to the associated guide rib.
Preferably, the branch bore is directed at an angle forwards. The coolant and lubricant stream can thus be directed to the cutting tip in a particularly simple manner.
In one embodiment of the microfinishing tool according to the invention, the branch bore and/or discharge bore associated with the guide rib has a smaller diameter than the bore associated with the cutter. In this way the cutter, which is subject to mechanically higher loads, is supplied with more coolant than the guide rib.
The microfinishing tool in accordance with the invention can be provided with one or more rigid cutters. It can also have one or more replaceable cutters and/or cutters mounted on a carrier. The cutter or cutters can be adjustable, i.e. it or they can be provided with a pre-cutting step.
In addition to one or more cutters provided at the periphery, an end cutter or an end cutting zone can be provided.
The taper screw can close off the axial coolant channel by its threaded end. This simplifies the manufacture of the tool, because the central bore for the cooling channel is then bored through right up to the tapered bore.
A matching to different cutter and guide rib shapes can advantageously be achieved if the taper screw has taper sections with different angles of taper. The cutters and guide ribs can be adjusted thus defined.
If the microfinishing tool according to the invention is provided with internal cooling, the axial coolant bore can issue into a distribution ring which is in front of the end of the taper screw opposite to the tip of the tool, and from which distribution ring the branch bores extend.
Suitable materials for the cutters of the microfinishing tool according to the invention are for example hard metal, cermet, ceramic, polycrystalline, natural or synthetic diamond, as thin film and thick film, or cubic boron nitride.
The guide ribs can consist of for example hard metal, cermet, ceramic, polycrystalline, natural or synthetic diamond, with or without coating.
In the microfinishing tool according to the invention one can arrange for the cutting head to be replaceable. In this way the tool can be utilised in a very versatile manner.
In one preferred embodiment of the invention the cutting head is fixed to the shank of the tool by means of a bayonet connection, or alternatively by means of a taper screw. Obviously, other adaptor connections are also possible.
The microfinishing tool according to the invention can have one, two, three or more cutters.
Preferably, at least one guide rib per cutter is provided. In one embodiment of a sinking and friction cutting tool, two guide ribs per cutter are provided.
The guide ribs are preferably provided between the cutters at the periphery. However, alternatively, a guide rib can be arranged axially offset relative to the associated cutter. In this way, the number of guide ribs per cutter and the desired guiding effect can be maintained in spite of greater numbers of cutters, and so a quiet, stable operation of the tool can be guaranteed in spite of high speeds of rotation and/or workpieces which are very hard.